New CPU - What about the fan?

Hi, I have just bought a new replacement CPU (it was dispatched today, so I haven't installed it) to upgrade my old Dell machine - a Dimension 4500. The CPU I bought is an Intel Pentium 4, Socket 478, Northwood processor, running at 2.8 Ghz, with a bus speed of 533 Mhz and a cache size of 512 KB. I bought it after reading on the Intel website (using thhe model number of my motherboard) it will work in my motherboard. Now, the processor I am replacing (the one that came with the PC) is an Intel P4 also, running at 1.8 Ghz, with a bus speed of 400 Mhz and cache size of 512 KB. Due to the fact the new processor is operating at a faster speed than the one it is replacing, it will undoubtedly by producing more heat than the old one. For this reason, I bought a new heatsink and fan for a socket 478 motherboard. After buying it I decided to do a test run installation, so I knew what to do when installing the new processor, and putting the new heatsink and fan on top of it. However, after then opening the computer it became apparent the new fan would not fit in my machine. The 4500, instead of having a heatsink sitting on top of the processor, and a fan on top of the heatsink, has a heatsink on top of the processor, and a fan vertically parrallel to the heatsink, and then a plastic "box-thing" that sits over them both, descibed as an air-flow compartment on the Dell webiste. So, this brings about the question of: if the fan doesn't fit, will the new processor not fit either? And if it does, will the old fan be able to keep it cool enough? If not, where can I buy a new fan and heatsink for an old Dell Dimension 4500, as I can't find one anywhere. Sorry this is such an essay, but I do need answers, and I felt I had to explain the whole situation. Please help.

take the air duct out then seat the new heatsink on not forgetting thermal compound . should run fine without the duct , as long as the heatsink is capable of cooling the cpu ,usualy stated on the box eg for proccesors upto 3800mhz to which i gather you bought one capable of the job cooling you new p4

just take the vent out

the vent used to be a home mod wereby putting a piece of plastic pipe over the vent holes at the back of the pc then positioning it over the cpu would increase airflow to which dell has implemented as a product. most people on here dont have one in their computers

If Dell thought it needed the 'airflow compartment' I wouldn't just throw it away. Fit the new cpu, refit the heatsink (thoroughly cleaned and new thermal paste applied)and refit the fan and plastic box as before.

Download Speedfan or something similar to monitor cpu temperature.

I'd be interested to know how big an improvement you see moving from a 1.8 to a 2.8 P4

from the dell websiteheres the changing heatsink diagramclick herechoose changeing the microprocessor optionas you already pointed out it is fed air from an off chip ie its not on the heat sink but drawing air in to blow over the sinkas from what i can see there would be no issue using your new heatsinkplease note as long as you have good ventilation in your case you wont run into heat the issue thus the reason dell implement the vent system as there really cramped add to the fact most dell dont have temp monitors (google for people who have removed this vent and also check out diffrent cooling methods and youll see ).but i still stick by if the heatsink is meant for a certain processor it should be used as it is picked for it heat disapataion suited to that hardware yes the 1.8 may be ample enough but how efficient is it going to be ? remember the cooler the component the longer life it has. that why we all buy bigger and quieter heatsinks instead of using the ones that come with the product even thou they are ample enough to run the proccesor also why zalman & sythe n other companys make a profit selling cooler solutions to reduce noise and make you chip last longer or overclockable

remember google is your friend and usually increase,s your knowledge on items your looking for